The present invention pertains to a system for facilitating an order change in the dry end conversion of a corrugated paperboard web. In particular, the invention relates to a method and apparatus for accomplishing an order change using a minimum slit head configuration slitter.
In a corrugator dry end, where a corrugated paperboard web is longitudinally scored and slit into multiple parallel output webs (or “outs”), the outs are directed through one or more downstream cut-off knives which cut the output webs into selected sheet lengths. When two cut-off knives are used, they are vertically separated and each is capable of cutting the full corrugator width web. A web selector positioned downstream of the slitter/scorer, divides the outs into two groups, one of which is directed to the upper cut-off knife and the other to the lower cut-off knife. Order changes must be effected while the upstream corrugator wet end continues to produce and deliver the continuous web to the slitter/scorer. An order change will typically result in a change in widths of the output webs; requiring redirection of at least a central portion of the web from one knife level to the other and possibly changes in edge trim widths as well.
The prior art has developed two basic order change systems for corrugator dry ends utilizing double level cut-off knives. One system is known as a gapless or plunge style order change system. In this system, there are two slitter/scorer stations immediately adjacent one another in the direction of web movement and through both of which the web travels. At order change, one slitter/scorer, operating on the currently running order, will lift out of operative engagement with the web, and the other slitter/scorer which is set to the new order alignment plunges down into operative engagement with the web. The result is a small order change region of corrugated web with overlapping slits and scores for both the running and the new orders.
FIG. 1 and FIG. 2 show typical configuration of gapless order change slitter scorers. The FIG. 1 concept has a slit and score axis 110 (110a), 111 incorporated on each of two side frames 112, 113 with a trim slit waste collect chute 114, 115 for each station. FIG. 2 shows a single side frame 116 design with a score/score 117, 117/slit/slit 118, 118a configuration and single trim slit waste collect chute 120.
The second basic order change system is known as a gap style system. In this system, there is normally a single slitter/scorer station 121 as shown in FIG. 3. At order change, an upstream rotary shear severs the corrugated board web laterally. After the shear severs the web, the current running order is accelerated through the slitter to pull a gap between this tailing out order and the severed web emerging from the shear. As the tailing out web clears the slitter/scorer, the operative slit and score heads 122, 123 are quickly repositioned in the open gap. The leading edge of the new order then enters the slitter/scorer.
The two station gapless slitter of FIGS. 1 and 2 is preferred because it allows order changes at higher speeds and because there are inherent advantages associated with never severing the corrugated board web. Mainly, the potential for skew of either the tailing or leading edge webs is eliminated. Tailout accuracy is not affected by drastic tailout acceleration and potential for jam-up of the leading edge of the new order web is eliminated. A disadvantage of the two station plunge slitter concepts is that there is a duplication of slit and score heads that increases the cost and complexity of the slitter/scorer.
In principle, it would be possible to implement a gapless order change with a single slit axis machine 124, as shown in FIG. 4. This would involve plunging some of the heads 125 on the slit axis into the board line 126 to slit the outs associated with the running order while positioning the unused heads for the next order. Then at order change, the new order heads 125 would plunge into this board line while the old order heads 125 were removed from operative engagement with the web. In practice, this is not possible because of physical space occupied by the slit heads and the sometimes small difference between old and new order slit positions.
An approach to use of a single axis slitter to accomplish a gapless order change of FIG. 4 is described in U.S. Pat. No. 6,684,749. This concept uses pre-positioning of unused slit heads to the extent possible based on physical interference between running order slit heads and desired placement position of new order slit heads. Then, at order change, a robot 127 quickly repositions slit heads 125 as required in an order change zone between the new and old orders. While this approach solves the problem of physical interference between slit heads on the single axis slitter 124, it can create a quite long order change zone of scrap board depending upon the speed of the corrugator and the number of heads 125 that need to be moved.